NAME AND COLOUR
STATS - Pretty much just ripped off the MM so feel free to alter or replace.
All Devils can see in the dark and all can move between Planes at will.
WHAT DO DEVILS WANT?
They want to be physically incarnated in the ‘real world’.
HOW LONG DOES IT TAKE A MASK TO DECAY?
I came up with some non-canon bullshit to kind-of make sense of this.
GETTING A MASK
D&D handles this kind of stuff quite well already. It’s a magical item and we have a thousand ways of placing those.
ASSUMING YOU HAVE A MASK, HOW DO YOU BIND A DEVIL?
HOW DOES A DEVIL GET RID OF ITS NAMES?
A devil knows its own names and knows that if it loses all its valid names then it is destroyed. It would help if it know which ones were the valid ones, but only the Binder can tell it that.